1. Field of the Invention
The present application relates to a compressed natural gas injector, which is tolerant of contamination in the gas.
2. Description of the Related Art
Compressed natural gas (hereinafter sometimes referred to as xe2x80x9cCNGxe2x80x9d) is becoming a common automotive fuel for commercial fleet vehicles and residential customers. In vehicles, the CNG is delivered to the engine in precise amounts through gas injectors, hereinafter referred to as xe2x80x9cCNG injectorsxe2x80x9d. The CNG injector is required to deliver a precise amount of fuel per injection pulse and maintain this accuracy over the life of the injector. In order to maintain this level of performance for a CNG injector, certain strategies are required to help reduce the effects of contaminants in the fuel.
Compressed natural gas is delivered throughout the country in a pipeline system and is mainly used for commercial and residential heating. While the heating systems can tolerate varying levels of quality and contaminants in the CNG, the tolerance levels in automotive gas injectors are significantly lower.
These contaminants, which have been acceptable for many years in CNG used for heating, affect the performance of the injectors to varying levels and will need to be considered in future CNG injector designs. Some of the contaminants found in CNG are small solid particles, water, and compressor oil. Each of these contaminants needs to be addressed in the injector design for the performance to be maintained over the life of the injector.
The contaminants can enter the pipeline from several sources. Repair, maintenance and new construction to the pipeline system can introduce many foreign particles into the fuel. Water, dust, humidity and dirt can be introduced in small quantities with ease during any of these operations. Oxides of many of the metal types found in the pipeline can also be introduced into the system. In addition, faulty compressors can introduce vaporized compressor oils, which blow by the seals of the compressor and enter into the gas. Even refueling can force contaminants on either of the refueling fittings into the storage cylinder. Many of these contaminants are likely to reach vital fuel system components and alter the performance characteristics over the life of the vehicle.
In general, fuel injectors require extremely tight tolerances on many of the internal components to accurately meter the fuel. For CNG injectors to remain contaminant tolerant, the guide and impact surfaces for the armature needle assembly require certain specifically unique characteristics. We have invented a CNG fuel injector which represents a significant improvement over presently known injectors while being tolerant to contaminants commonly found in compressed natural gas. We have also invented a method of directing compressed natural gaseous fuel through such injectors in a manner to promote efficient and effective firing without misfire.
The invention relates to an electromagnetically operable fuel injector for a gaseous fuel injection system of an internal combustion engine, the injector having a generally longitudinal axis, which comprises a ferromagnetic core, a magnetic coil at least partially surrounding the ferromagnetic core, an armature magnetically coupled to the magnetic coil and being movably responsive to the magnetic coil, the armature actuating a valve closing element which interacts with a fixed valve seat of a fuel valve and being movable away from the fixed valve seat when the magnetic coil is excited. The armature has a generally elongated shape and a generally central opening for axial reception and passage of gaseous fuel from a fuel inlet connector positioned adjacent thereto. The fuel inlet connector and the armature being adapted to permit a first flow path of gaseous fuel between the armature and the magnetic coil and a valve body shell as part of a path leading to the fuel valve. At least one first fuel flow aperture extends through a wall portion of the armature to define a second flow path of gaseous fuel as part of a path leading to the fuel valve.
In the preferred embodiment, the armature defines at least one-second aperture in a wall portion thereof to define a third flow path of gaseous fuel as part of a path leading to the fuel valve. The at least one second aperture is oriented at a generally acute angle with respect to the longitudinal axis. Further, the fuel inlet connector and the armature are a spaced to define a working gap therebetween and are adapted to permit the first flow path of gaseous fuel within the working gap. The fuel injector further comprises a valve body positioned downstream of the armature and having at least one aperture in a wall portion thereof for reception of fuel from at least two of the flow paths of gaseous fuel from the armature and the fuel inlet connector.
Further, a valve body shell at least partially surrounds the armature and the valve body, the valve body shell defining a radial space with the armature for passage of the first flow path of gaseous fuel between the armature and the valve body shell. The fuel inlet connector is positioned above the armature and is spaced from the armature by a working gap, the fuel inlet connector defining a through passage for directing fuel toward the armature and the fixed valve seat.
The fuel inlet connector comprises an upper end portion adapted for reception of gaseous fuel from a fuel source, and a lower end portion for discharging gaseous fuel, the lower end portion having a lower surface which faces an upper surface of the armature, the lower surface of the fuel inlet connector having a plurality of radially extending raised pads defined thereon, the pads having recessed portions therebetween to permit fuel to flow therethrough and across the working gap defined between the fuel inlet connector and the armature.
The armature defines at least one first and at least one second fuel flow aperture extending through wall portions thereof, the at least one first and at least one second aperture oriented at an acute angle with the longitudinal axis, and positioned for directing fuel therethrough toward the fixed valve seat. The lowermost surface of the fuel inlet connector and the armature are adapted to permit gaseous fuel to flow across the working gap and between the armature and the magnetic coil whereby at least three fuel flow paths are permitted. Preferably lowermost end portion of the fuel inlet connector has a generally chamfered configuration along the lowermost outer surface thereof. The generally chamfered portion of the fuel inlet connector preferably has a generally arcuate cross-section.
The valve-closing element is a valve needle adapted for selective engagement and disengagement with the fixed valve seat and is attached to the armature by crimped portions of the armature. A fuel filter is positioned at an upper end portion of the fuel inlet connector for filtering fuel prior to reception by the fuel inlet connector. The fuel inlet connector includes a lower surface portion having a plurality of radially extending grooves defining a corresponding plurality of radially extending raised pads so as to reduce the effective surface area of the lower surface portion of the fuel inlet connector facing the armature to thereby permit the gaseous fuel to flow generally transversely in the working gap, the transverse fuel flow thereby preventing accumulation of contaminants in the working gap. The generally radially extending pads preferably have a generally trapezoidal shape, but may be of various shapes, depending upon the circumstances or results desired. Further, the fuel injector is applicable to liquid fuel systems such as gasoline, as well as with the preferred CNG systems.
The valve closing element is a generally elongated valve needle having a spherically shaped end portion and configured and adapted to engage a frust-conically shaped fixed valve seat to close the valve, and movable therefrom to open the valve to permit fuel to pass therethrough toward the intake manifold of the internal combination engine. The valve needle is connected to the lower end portion of the armature by crimped portions. The resilient device to move the armature to close the valve is a coil spring in engagement at one end with the fuel inlet connector and at the other end with the armature to bias the armature downwardly toward the valve seat. The armature includes at least two of the first apertures extending through wall portions thereof and generally transverse to the longitudinal axis for receiving fuel from the generally axial elongated central opening. The armature may alternatively define a plurality of the first apertures for receiving fuel from said generally axial elongated central opening. The armature may also define a plurality of the second apertures, at least certain of the second apertures extending at a generally acute angle to the longitudinal axis to receive fuel from the generally central opening.
A method is disclosed for directing gaseous fuel through an electromagnetically operable fuel injector for a fuel system of an internal combustion engine, the injector having a generally longitudinal axis, and including a fuel inlet end portion and a fuel outlet end portion, a fuel inlet connector positioned at the fuel inlet end portion and having a fuel inlet end portion and a fuel outlet end portion, an armature positioned adjacent the fuel outlet end portion of the fuel inlet connector and having a generally central elongated opening for reception of fuel from said fuel inlet connector, the armature being spaced from the fuel inlet connector to define a working gap to permit movement of the armature toward and away from the fuel inlet connector to selectively open and close a fuel valve to permit gaseous fuel to pass therethrough to an air intake manifold. The method comprises, directing the gaseous fuel to pass axially through the fuel inlet connector, directing the gaseous fuel to pass from the fuel inlet connector to the generally elongated central opening of the armature in an axial direction toward the fuel valve, directing at least a portion of the fuel flow from the fuel inlet connector to the armature to flow generally transversely across the working gap, and diverting at least a portion of the flow of gaseous fuel passing through the armature to flow in a direction away from the axial direction. The step of directing the gaseous fuel passing through the armature to flow in a direction away from the axial direction is preferably accomplished by directing the gaseous fuel through at least one first aperture provided in a wall portion of the armature. Preferably the at least one first aperture in the wall portion of the armature extends generally transverse to the axial direction. A lower end portion of the fuel inlet connector preferably faces an upper end portion of the armature and is configured to permit the gaseous fuel to flow from the fuel inlet connector to be directed transversely across the working gap. Preferably at least a portion of the gaseous fuel flowing in the armature is permitted to pass through at least one second aperture in a lower wall portion thereof, the at least one second aperture extending at an acute angle to the longitudinal axis, whereby at least three separate fuel flow paths are established. The injector preferably comprises a magnetic coil system and said armature is magnetically coupled to the magnetic coil system to cause the armature to move toward and away from the fuel inlet connector. At least one of the fuel flow paths is located between the armature and the magnetic coil of the magnetic coil system, as well as between the armature and a valve body shell at least partially surrounding the armature. The at least one first and second apertures in the armature are preferably from about 1 to about 2.0 mm in diameter. Further, predetermined numbers of the first and second apertures are provided and the diameters thereof are predetermined to establish a predetermined number of fuel flow paths and volumetric flow rates thereof.